The impact of dietary protein intake on urinary creatinine excretion in a healthy pediatric population.

Abstract

The aim of the study was to investigate the effect of daily protein intake on urinary creatinine (CR) excretion in healthy children. In a cross-sectional study, 24-hour urinary CR excretion rates were measured in 350 children aged 4 to 13 years. Body composition was assessed according to anthropometric measurements, and intake of protein was estimated from dietary records. CR excretion adjusted for fat-free mass (FFM) showed a strong age dependency and correlated clearly with total protein intake and animal protein intake. Stepwise regression analyses revealed that age was the main predictor; however, animal protein intake improved the proportion of explained variance in FFM-related CR excretion. Comparisons of urinary CR output in subgroups of children with low (1st tertile) or high (3rd tertile) animal protein intake showed that on average, a difference of about 9% in CR excretion corresponded to a difference of 1.1 g/kg of body weight per day of animal protein intake. Animal protein intake must be taken into account when urinary CR output is used for evaluating body composition in children. Additionally, the finding of a clearly stronger increase in urinary CR than in FFM with age offers an explanation for the commonly observed phenomenon of a decreasing ratio of numerous urinary analytes related to CR during childhood.